Great analysis, but I think the writer overlook one MASSIVE additional item (unless it was there and I missed it).
What do the Blue Insurgents think the armed inner city denizens will be doing during this civil war? Grab their Saturday Night Specials and don a blue uniform and the resplendent cap and pony-tail?
NO!! They will take advantage of the instability (and the assumed conscription of LEOs) to RIOT AND LOOT!!
So not only does the Blueies have to deal with an armed, trained (for the most part -- more on that in a moment), and disbursed Red America, but they will also have to dedicate forces to TRY to protect life and property in the very heart of their "strongholds." And those rioters, once emboldened will fan out to the affluent suburbs with nothing to stop them.
As to well-trained let me summarize it this way: Proper use and knowledge of weaponry is an admired trait in Red America. Anyone who handles a weapon improperly is subject to derision and shame. In Blue America the non-veterans for the most part think shooting a gun with the grip parallel to the ground is cool and the proper way to do so.